The IMS (IP Multimedia Subsystem) of 3rd generation mobile networks provides a variety of services to the connected devices. The services comprise the control and provision of media data of various types, for example audio data, video data, a combination of audio and video data (e.g., for video telephony), text data, application data, etc.
The IMS is thus a prominent example for a multimedia-enabled network (the Internet is another example of a multimedia-enabled network). The control of the services requires appropriate signalling mechanisms to ensure proper end-to-end transport of the media data. The IMS utilizes the SIP (Session Initiation Protocol) for these purposes. Within the SIP framework, user agents act on behalf of their users. User agents initiate requests and may usually be their final destination. Typically, but not exclusively, a user agent is a piece of software implemented on the user equipment or one of the user devices of the user. IP (Internet Protocol)-Phones or conferencing software are examples of user agents which may be implemented on mobile phones, smartphones, but also notebooks and other user terminals, user devices or items of user equipment enabled for communication over a network.
The principal role of SIP is to set up sessions or associations between at least two service-terminating devices, for example user devices but also server systems. Once a session is established, media data may be exchanged between the devices. For session establishment, session requests have to be routed through the network. To this end, SIP introduces a number of serving entities in the network, comprising a registrar server (including a location server), which keeps track of users after their registration in the network; a proxy server, forwarding as an application-layer router the SIP requests and responses; and/or a redirect server, receiving a request and returning a location of a SIP user agent or server where the requested user might be found. The media data of a session itself might be forwarded directly between the user agents. The serving entities may be part of or may be collocated to a CSCF (Call State Control Function) of the IMS domain.
Whereas the SIP protocol controls establishment and teardown of sessions, further protocols are required to, for example, accomplish the media data transport. The SDP (Session Description Protocol) and/or RTP (Real Time Protocol) or other protocols may be used for this purpose, which itself may make use of IP-UDP (User Datagram Protocol) communications or IP-TCP (Transmission Control Protocol) connections. Therefore, if not otherwise stated, the usage of the term ‘SIP’ herein is meant to denote the protocol suite of SIP for control of multimedia services and not only the SIP protocol itself.
Within the SIP framework, the addressing of another user, more precisely the addressing of one of the one or more items of user equipment of that user, may be achieved in different ways: as a first example, a SIP URI (Uniform Resource Identifier) of the user may be used which specifies an address in the format ‘sip:user@network’, the format structure being known from email-addresses. As a second example, an URI or URL (Uniform Resource Locator) may be used which is associated directly with a user device or user equipment of the user. Routing of service requests (service invocations) based on a user-related URI includes to resolve the user-related URI to the address associated to the correct UE of the user. This task may be performed with the help of a proxy server or redirect server.
A user agent of a device is the logical session endpoint for a service, i.e. the user agent terminates the service. For generating media data, the device has to comprise further hardware and/or software components, for example microphones or cameras for acquiring still and/or moving images, but also storage components which may, for example, be adapted for providing streaming media data (e.g. a DVD and a DVD drive providing a video stream). Still further, a media resource may also be the destination of a media stream, for example a storage device or storage component adapted for storing media data, e.g. a DVD-burning drive and/or the DVD adapted for insertion into the drive.
These media resources may have been integrated into the (user) device, which means that the user equipment has been adapted to access the integrated media resource and to provide the media data generated by the resource to the multimedia network. For example, the manufacturer of the user equipment may have configured a user agent specifically for controlling an integrated resource. Due to this specific adaptation of user equipment and integrated media resource, the capabilities of the integrated media resource may be announced to the network as capabilities of the user equipment.
Many user devices offer interfaces for attaching external hardware or software components or devices. For example, many mobile phones or notebooks offer one or more wireline or wireless interfaces of the following kinds: USB (Universal Serial Bus), Bluetooth, Serial or Fast-IR (Infrared), WLAN, FireWire, etc. These interfaces may be used to locally attach hardware devices, for example, home electronics (e.g., entertainment systems or home appliances), computing devices (e.g., personal computers), or mobile devices, which in turn may incorporate a camera, an IP phone, a media content player or similar devices. The device interfaces may also comprise interfaces for remote communication, for example IP-based communication, with a remote hardware, for example a remote computer, which may include a media resource.
If an interface for attaching external components is provided, the service-terminating equipment may also be adapted for controlling an attached media resource. For example, a mobile phone may be adapted to control an attached camera, such that the camera acquires a video sequence and sends the image to the phone. A user agent implemented in the mobile phone may then provide the acquired image to another device via an appropriate service of the network.
However, the attached media resource itself and its properties are not known in the network. For example, in an IMS network using the SIP protocol suite, a user agent may register on behalf of a user equipment in the network, announcing thereby the particular media-related capabilities of the UE. But there is no mechanism specified within the SIP framework to register an external media resource for the purpose of enabling access to it from or over the network. The SIP framework also provides for presence servers in the network as a possibility to announce UE capabilities for discovery by other UEs, see the 3GPP (3rd Generation Partnership Project) TS (Technical Specification) 23.141 and TS 24.841. The presence service, however, does not allow to announce capabilities of an attached media resource. Consequently, without a registration in the network, the resource cannot be accessed by other devices via the network. As an example, without registration, a discovery of capabilities offered by the attached media resources is not possible.
More and more mobile devices incorporate interfaces for WLAN (Wireless Local Access Networks) or similar techniques allowing to establish local ad-hoc networks for interconnecting several terminals with each other and further external media resources, wherein an access to a media resource attached to another UE may be possible. However, there is no possibility to date to connect from a multimedia network as IMS to such a local network and access the media resources.
The possibility to access media resources attached to a network-registered device via a network would thus add a diversity of use cases to the application field of multimedia networks. Accordingly, there is a need for a technique for providing access from an access-requesting entity via a multimedia-enabled network to a media resource controllably attachable to a network-registered device.